The present invention relates generally to circuitry for detecting and measuring the current supplied to a load, and more particularly to an isolator circuit for providing an output signal to a relatively low power circuit which is proportional to the current supplied to the load from a power circuit.
In a motor drive system where, for example, a DC motor is supplied power from a thyristor type of static converter, control of the motor is achieved by sensing either the motor armature current of field current and generating therefrom a signal indicative of actual motor operation. This signal is then compared to a desired operating condition reference signal, with an error signal being developed therefrom which is utilized to control the thyristor converter. Such systems find wide application and take many different circuit configurations depending upon the specific task contemplated. Because of the relatively large currents which often are encountered on the power side of the motor drive system, it is vitally necessary to be able to sense these currents in a safe and reliable manner. Transformers obviously can fulfill the need where alternating currents are encountered; however, where DC currents are sought to be sensed, more sophisticated means must be resorted to.